Tube



May 7, 1946. E. MURDOCK TUBE Filed Jan. 11, 1944 INVENTOR CLAYTON E. MURD CK HIS ATTORNE ii atentcd May 7, 1946 TUBE Clayton E. Murdock,

Eitel-McCullough,

Millbrae, Calm, assignor to Inc.,

San Bruno, Calla, a

corporation of California Application January 11, 1944, Serial No. 517,871 12 Claims. (Cl. 250-275) My invention relates to vacuum tubes, and more particularly to an improved stem structure for such tubes.

It is among the objects of my invention to provide a coaxial type of stem for supporting an electrode, such as a cathode, in which the comprises a part of the tube envelope.

Another object is to provide a stem structure of the character described, wherein the stem also forms the base of the tube and furnishes terminals for the electrode.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention as I may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawing:

Figure 1 is a vertical sectional view. of tube portions embodying my improved stem; and

Figure 2 is a horizontal sectional view of the cathode support, taken in a plane indicated by line 2-2 of Figure l. y

In terms of broad inclusion, my improved tube comprises an envelope enclosing an electrode, and a stem structure comprising a pair of coaxial metallic members supported by and forming part of the envelope, and means connecting the electrode to the members, each of the members having a portion exposed externally of the tube to provide terminals for the electrode. Improved means are also provided for supporting the electrode on the stem structure, which supporting means also includes a spring tensioning device for the electrode.

In greater detail, and referring to the drawing, my tube comprises an envelope body 2 of vitreous material, such as glass, enclosing an electrode 3. My improved stem structure is particularly suited for supporting a filamentary cathode, and this type of electrode is illustrated. Only the lower portions of envelope body 2 are shown because this is sufilcient to disclose the improvements. It is understood that other electrodes such as a grid and mode may be provided and mounted in the envelope in any suitable manner.

The improved stem comprises a pair of coaxial metallic members including an outer tubular member 3 projecting from the envelope body and an inner solid member 4 projecting from the tubular member. These parts may be of any suitable metal, such as Kovar, adapted for sealing to glass. Outer member 3 is open-ended and preferably has its end portions inturned on a smooth curve, the upper end of the member extending somewhat into envelope body 2. Inner stem per portionsof outer stem member 8, and a spacing ring I of vitreous material such as glass is interposed between the two members. This spacer is fused to the lower end of outer member 3 at seal 8, and to the intermediate portions of inner member 4 at seal 9. The entire stem structure is thus supported by and forms part of the envelope.

Cathode 3 is made in say four sections, each comprising a plurality of vertical wires i I of thoriated tungsten. The upper ends of the wires in all the sections are joined, preferably by welding the wires to the rim of a cup-shaped metallic cap l2. The lower ends of the wires in each section are welded to an arcuate end piece i3, which pieces are spaced and arranged in a circle so that the vertical bars of the filament lie in cylindrical formation.

The lower ends of a pair of oppositely disposed filament sections are supported by and electrically connected to the outer stem member by metal brackets i4 welded to end pieces i3 and to the periphery of a metallic collar it which in turn member 4 of the stem is spaced from and extends upwardly into the outer member. A seal 6 is formed between the envelope body 2 and the upis welded to the intumed upper end of member 3. The lower ends of the other pair of filament sections are supported by and electrically connected to the inner stem member by metal'brackets i'i welded to end pieces I! and to a metallic extension sleeve it on member 4. Pairs of the filament sections are thus connected in series between the stem members through which the heating current is supplied. This cathode structure has the advantage of compacting a multiplicity of filament wires in a relatively small circle, whereby a large amount of electron emitting surface is made available.

My improved stem also forms the base of the tube, it being seen that members 3 and 4 have portions exposed externally of the tube to provide terminals for the cathode. This base may be insertedin any suitable socket adapted to make contact with outer member 3 and the central prong member 4. My stem therefore eliminates the need for a separate base cemented to the envelope, which is the usual practice.

I also provide means for supporting the upper end of the cathode and for tensioning the wires in the filament sections to aid in maintaining alignment. For this purpose a center rod 2| is imbedded in a body 22 of vitreous material suchas glass provided in a recess 23 in the upper end of inner stem member 4. This center rod projects axially through the cathode and through a hole in top cap i2, the latter being slidable along the rod. v A'pusher sleeve 24 encircling the center rod bears upwardly against cap i2, and a spring 26 is interposed between the lower end of this sleeve and a stop 29 on the rod. Cups 21 provide bearing surfaces for the ends of the spring. It will be noted that spring 28 is disposed down in the stem structure away from the heat zone about the cathode, so that the spring is not subjected to temperatures which would destroy its resilience.

I claim: 1. A cathode structure comprising a filament having sections joined at the top and spaced at the bottom, a pair 01 coaxial metallic stem members, means connecting the lower end of one of the sections to one of said members, and means connecting the lower end of another section to the other member, and filament tensioning means supported on one of said stem members.

2. A cathode structure comprising a filament having sections joined at the top and spaced at the bottom, a pair 01 coaxial metallic stem members, means supporting the lower end of one of the sections on and electrically connecting it to one of said members, means supporting the lower end of another section on and electrically connecting it to the other member, and means insulated from and mounted on one of said members for supporting the upper joined ends oi. said sections.

3. A cathode structure comprising a filament having sections joined at the top and spaced at the bottom, inner and outer metallic stem members, a spacing ring of vitreous material interposed between and sealed to said members, a center rod projecting upwardly from the inner member for supporting the upper joined ends of said sections, a body of vitreous material interposed between and sealed to said rod and inner member, and means connecting the lower ends of said sections to said members.

4. A cathode structure comprising a filamenthaving sections joined at the top and spaced at the bottom, inner and outer metallic stem members, a spacing ring of vitreous material interposed between and sealed to said members, a center rod projecting upwardly from the inner member for supporting the upper joined ends of said sections, a body of vitreous material interposed between and sealed to said rod and inner member, spring pressed means slidable along the center rod for tensioning the filament sections, and means connecting the lower ends of said sections to said members.

5. A cathode structure'comprising a filament having sections joined at the top and spaced at the bottom, inner and outer metallic stem members, a spacing ring of vitreous material interposed between and sealed to said members, the

inner member having a recess therein, a body of vitreous material in the recess, a center rod imbedded insaid body and projecting upwardly from the inner member for supporting the upper joined ends of said sections, and means connecting the lower ends or said sections to said members.

6. A tube for insertion into a socket, comprising an envelope enclosing an electrode, a contact stem structure comprising a pair of metallic members supported by and forming part of said envelope adjacent one end thereof, a sealing ring of vitreous material interposed between said members, the largest external diameter of said ring being less than that of one of said members, and means connecting the electrode to and supporting it on said members, each of said members having a portion exposed externally of the tube to provide terminals for said electrode.

7. A tube for insertion into a socket, compris.

ing an envelope enclosing an electrode, a contact stem structure comprising a pair of coaxial metallic members supported by and forming part ofsaid envelope adjacent one end thereof, a sealing ring of vitreous material interposed ,between said members, the largest external diameter of said ring being less than that of one or said members, and means connecting the electrode to said members, each of said members having a portion exposed externally of the tube to provide terminals for said electrode, said stem structure providing a closure for an end oi the envelope.

8. A tube for insertion into a socket, comprising an envelope enclosing an electrode, a contact stem structure comprising a tubular member and a prong member both supported by and forming part or said envelope, a sealing ring of vitreous material interposed between said members, the largest external diameter of said ring being less than that of the tubular member, and means connecting the electrode to said members, each of said members having a portion exposed externally of the tube to provide terminals for said electrode, said prong member projecting from the tubular member and extending axially beyond the remaining portions of the envelope,

9. A tube for insertion into a socket, comprising an envelope having a bodyot vitreous material, an electrode in the envelope, an outer tubular stem member of metal sealed and Projecting from said body, an inner stem member or metal coaxial with the tubular member, a sealing ring of vitreous material interposed between said members, the largest external diameter of said ring being less than that of said outer member, and means connecting the electrode to said mem bers, said inner stem member having a section of solid cross-sectional area to form a closure mem her at an end of the envelope.

10. A tube for insertion into a socket, comprising an envelope having a body of vitreous mate. rial, an electrode in the envelope, an outer tubular stem member of metal sealed to and project ing from said body, an inner stem member oi metal coaxial with the tubular member, a sealing ring of vitreous material interposed between said members, the largest external diameter of said ring being less than that oi. said outer member, a support for one end of the electrode mounted on said tubular member, and a support for the other end of the electrode mounted on said inner mem ber.

11. A stem structure for a tube for insertion into a socket, comprising a pair of coaxial metallic stem members adjacent one end of the tube, a sealing ring of vitreous material interposed between said members, the largest external diameter of said ring being less than that of one of said members, each of said members having portions exposed externally of the tube, one of said members having a section of solid cross-sectional area to forma closure member across said vitreous ring.

12 A cathode structure comprising a filament having longitudinally extending wires, a pair of coaxial metallic stem members, means connecting the lower ends of certain of said wires to one of the members, means connecting the lower ends of other wires to the other member, and filament tensioning means supported on one only of said stem members and connected to the upper ends 01 said wires.

CLAYTON E. MURDOCK 

